Novel calmodulin mutations associated with congenital long qt syndrome affect calcium current in human cardiomyocytes

Background Calmodulin (CaM) mutations are associated with cardiac arrhythmia susceptibility including the congenital long QT syndrome (LQTS). Objective To determine the clinical, genetic and functional features of two novel CaM mutations in children with life-threatening ventricular arrhythmias. Methods The clinical and genetic features of two congenital arrhythmia cases associated with two novel calmodulin gene mutations were ascertained. Biochemical and functional investigations were done on the two mutations. Results A novel, de novo CALM2 mutation (D132H) was discovered by candidate gene screening in a male infant with prenatal bradycardia born to healthy parents. Postnatal course was complicated by profound bradycardia, prolonged QTc (651 msec), 2:1 atrioventricular block and cardiogenic shock. He was resuscitated and was treated with a cardiac device. A second novel, de novo mutation in CALM1 (D132V) was discovered by clinical exome sequencing in a three year-old boy who suffered witnessed cardiac arrest secondary to ventricular fibrillation. ECG recording after successful resuscitation revealed a prolonged QTc of 574 msec. The Ca2+ affinity of CaM-D132H and CaM-D132V revealed extremely weak binding to the C-domain with significant structural perturbations noted for D132H. Voltage-clamp recordings of human induced pluripotent stem cell (iPSC) derived cardiomyocytes transiently expressing wildtype or mutant CaM demonstrated that both mutations caused impaired Ca2+ -dependent inactivation (CDI) of voltage-gated Ca2+ current. Neither mutant affected voltage-dependent inactivation. Conclusion Our findings implicate impaired CDI in human cardiomyocytes as the plausible mechanism for LQTS associated with two novel CaM mutations. The data further expand the spectrum of genotype and phenotype associated with calmodulinopathy.